Depends on a lot of things. Some guns safety mechanisms are different than others. Striker-fired handguns (such as Glock 22/23's which are what the FBI carries) are theoretically capable of doing this but there's a lot of debate over if it will really happen. However, they have firing pin safeties which stop this from happening. Those Glocks also have trigger safeties rather than traditional toggles. He could have been carrying a personal weapon for all we know.

That said, most guns will not discharge if dropped in 90% of circumstances. Most importantly, if you happen to drop a gun don't attempt to catch it. Let it fall and hit the ground. By trying to catch it you're way more likely to accidentally fire it.